Using superconducting circuits to manipulate electrons. Ions traps to, well, trap atoms in a vacuum. Quantum annealing, whatever that complicated, mindboggling process is. Quantum dots etc. There are many ideas out there as to how qubits will be controlled to create the best, and most efficient, quantum computers.

Photons

Another way is by using photons as qubits. In this method, qubits are the train that carries the quantum information. As of 2019, there are a number of startups in the space that use this approach to build their architecture, from QuiX in the Netherlands, Xanadu in Canada to PsiQ in the UK. These are joined by the large Japanese corporation, NTT. Although not as common in the space as some of the other approaches, photonic QC does have its advocates around the globe.

‘Light is something like raindrops—each little lump of light is called a photon—and if the light is all one color, all the “raindrops” are the same.’

—Richard Feynman, QED: The Strange Theory of Light and Matter

Quandela

Quandela, a French company headquartered in Paris, is another one to join the stable of companies which believe photons are the way to go to create the best, most reliable quantum computers.

the fabrication of performing devices for the research in quantum photonics and quantum information

By developing its ideas using a single-photon approach, Quandela hopes to achieve the emission of individual photons that possess characteristics that are identical to each other taken from quantum dots at very cold temperatures. Adopting this technique, the startup can collect single photons in a very efficient way. This also eliminates one of the scourges of the industry — reducing decoherence of the system.

As of late 2019, the company has yet to get any VC funding (that is according to their website and Crunchbase), though they have received funds from the European Union’s Horizon 2020 research and innovation program.

Giesz, who is CEO/CFO, leads his team of CTO Somaschi and Scientific Advisor Senellart into the quest to commercialize single-photon sources. Yet, as with the other approaches in the space, optical QC has its critics as well as supporters. They are hoping, however, with no decoherence, easy single-qubit gates — which operate at room temperature — as well as the quick operation times, they can sway investors into handing over cash.

To learn more about Quandela’s approach, you can read this whitepaper here on the efficiency of a single-photon source